A Puzzling Problem.......

Post by **mrmorrisminor** » Sun Aug 09, 2009 6:45 pm

We have been trying to solve an intermittent fault on my brother's standard 1098 engine for some time but to no avail.

The car starts and runs beautifully, at tick over there is a smooth exhaust note. It acceleates well round town, even if you really give it some stick in 3rd to get up a hill.

It even cruises happily on A roads..... until you go over 60mph. Then it starts to faulter..... cough and generally mess about until you ease down to 55..... and off you go again. The car has been from South London to the New Forest twice, laden with 4 passenges, a dog and a roof rack full of stuff and has made it without a cough....... but try going over 60....no way!

So far we have:

-Checked the timing
-Checked the point gap
-Cleaned fuel filter
-Checked for vaccume in fuel tank (petrol spills out of filler when you corner sharply!)
-Cleaned carb, fitted new float valve, jet
-Checked that piston rises freely and dash pot has oil
-Fitted new air filter
-Checked fuel flow from pump (gushes out and pump runs flat out)
-Changed plugs
-Changed condenser
-Renewed spade connectors to coil and distributor

The coil was new when I rebuilt the car 2 years ago as were all leads etc

I am now getting a little frustrated having tried most of the obvious bits! It does not seem 'rev' related as you can drive the car very hard in 3rd up a long hill ok, it has only faultered once doing this when fully laden. It feels to me to be some kind of fuel starvation but I am now at a loss!
Anyone got any ideas?

Post by **bmcecosse** » Sun Aug 09, 2009 6:51 pm

Wow - you do seem to have covered most angles. I guess it just knows the speed limit is 60 - unless on dual carriageways.
So - assuming it's not that clever - could you check if the vacuum advance in the dizzy is working ? Suck the tube and watch if the baseplate moves (be ready to spit!). And - are the centrifuagl advance weights and springs properly connected below the base plate - if you twist the rotor arm, does it spring back ? Also check the valve gaps - and is the coil connected right way round - ie -ve terminal to points assuming neg earth car? And - what colour are the plugs after running it hard and switching off? Also what plugs are you using ?

Sun Aug 09, 2009 8:54 pm

i had what sounds like this problem on a saloon i bought a few years ago. it was eventually resolved by replacing the carb completely.. might be worth a try.

Post by **ssnjimb** » Sun Aug 09, 2009 10:25 pm

Its far cheaper to fit a service kit to begin with as carbs rarely give trouble as there are only 2 or 3 moving parts.

Once it has new gaskets etc see how it is.

Post by **kennatt** » Mon Aug 10, 2009 8:11 am

fuel level in carb bowl maybe

try pulling the choke out when it hapens ,see what result,would confirm fuel starvation

linearaudio · Post by **linearaudio** » Mon Aug 10, 2009 8:22 am

Is the new coil you fitted definitely a 12V one?? I had problems like that when inadvertantly fitting a ballast type. Touch the coi after a runl- if it's uncomfortably hot, then it's a ballast one.

Also, check the little earth wire inside the dizzy. If that is bruck then curious things can occur, depending on if you are under load or not, as the base plate moves round with vacuum advance, creating differing electrical resistance to earth due to dirt/ grease between the parts.

Post by **Dru** » Mon Aug 10, 2009 9:01 am

is there a temperature element in the faltering? -I once had an intermittent problem with a Ford Escort faltering at speed, which mystified me and turned out to be carb icing. Problem resolved by ensuring supply of warm air to carb inlet...

...probably highly unlikely, but I thought I'd mention it...

Post by **ColinP** » Mon Aug 10, 2009 12:20 pm

Hi,

just a couple of odd thoughts....

When you changed the air filter - did you notice the breather pipe?
I once had an air filter where the breather pipe hole had been enlarged. Running at 60 ish the "suck" of the inlet started to pull oil up the breather pipe (it ended up dribbling from the filter!).

Might be worth checking out the engine brether system (type is age dependant)

Similarly - woth checking the vacuum advance/retard action - and pipework.

HTH
Colin

Post by **mrmorrisminor** » Mon Aug 10, 2009 4:10 pm

Thank you for all the suggestions.

-I can confirm that it is running on Champion n9yc plugs, as our other minor does.
- I have checked the braded earth wire inside the distributor and all seems good
-The vaccum advance appears to be ok, can suck on the hose and see movement the other end.
-Pulling the choke does not improve matters (although if the fuel level is wrong in the float chamber this maynot increase the fuel flow enough i suppose)
-The coil does seem a little on the warm side, have double checked all wiring to it and all seems good.
-Had a look again at the float, the level of petrol in the chamber was about half full once I had removed the float.
-There is a slight oiliness inside the air filter housing but the filter is clear of oil and none is dripping out.

So think my next step is to swap the coil. If this does not work I'll investigate further the fuel level in the float chamber.

Although one positive side effect is that said minor and young driver are restricted to a sensible speed! I just keep reminding him how much petrol he's saving

Post by **Mick_Anik** » Mon Aug 10, 2009 4:36 pm

I've mentioned this recently - I once had a similar problem, which in the end I believed I traced to a plug which was failing only at a certain rev level.
Probably a hairline crack in the insulator. It passed the 'out of engine' test, ie it sparked. But that doesn't tell you what's going on when it's in action on the road.

I say "I believed".....no way of knowing for sure - coincidences happen. But I just changed the one plug.......end of problem!

Post by **Peetee** » Mon Aug 10, 2009 5:30 pm

Check the throttle cable location is sound. Check if the outer housing is seated correctly at both ends and that the nipple is sitting correctly in the pedal arm. Likewise, see if the carpet is interfering with the arm. When I fitted underlay I had to reset (bend

) the arm to get full throttle movement.

Post by **Mick_Anik** » Mon Aug 10, 2009 5:50 pm

More thinking going on.....(I seem to be having a day off here - I'm posting like there's no tomorrow!)

Maybe the piston in the carb is suddenly flying up - scoring perhaps? Is it filled with the correct grade oil? Maybe try emptying it, and topping up with gear or axle oil, which is thicker. Only for the test, though, it may be too thick for normal use. Any views on this point?....I'm just thinking laterally here.
If you do want to empty the dashpot, just push the piston up sharply with a finger - with a rag covering the hole to catch the stream of oil - it can go a long way, as I found out last week!

Post by **mrmorrisminor** » Mon Aug 10, 2009 8:12 pm

Thank you

-It has had a new set of plugs but no joy.

-The problem is that the engine begins to caugh and faulter above 60 rather than just not accelerate, but pulls well when driven hard to high revs in gears 1-3.

The quest continues

Post by **MarkyB** » Mon Aug 10, 2009 8:35 pm

When you say "Cleaned fuel filter " is that the one in the petrol pump or on the one on the sender unit/petrol pickup?
The other one must be worth a look.

Post by **Dean** » Mon Aug 10, 2009 9:33 pm

mrmorrisminor wrote: -The problem is that the engine begins to caugh and faulter above 60 rather than just not accelerate, but pulls well when driven hard to high revs in gears 1-3.

I'm guessing the issue is there when you rev through the gears, but you rev through it. In fourth above sixty you are holding the revs which makes it more pronounced.

I Don't think you have eliminated all earthing/electical issues:

-Make sure all plugs make a good sound contact with a clean block when tightened,
-You haven't mentioned the rotor arm? Is that new or old? Does the pin in the top of dizzy cap make good positive contact with the rotor arm? Does this pin spring in and out freely, emory every contact clean.
-Be sure you aren't getting a short in the points area? Any fraying wires could create a cross connection simultaneously while running.

Do you own an electrical tester? Make sure you are getting equal resistance through each of the four HT leads to the plug electrodes from inside the dizzy cap. To do this set the tester to OHMS. It's quite easy to not push the leads into the dizzy cap correctly. Don't forget to check the lead from the cap to the coil.

I need a rest after that! Sorry if any of this seems patronising, i've been there myself and it was a dodgy plug!!!

Post by **Mick_Anik** » Mon Aug 10, 2009 9:42 pm

I have the feeling that this problem is 'one of those'......the source of the trouble is going to be something really stupid. Like, everything is spot on, only.......................

"Well, blow me! They'll never believe me down at the club!"

I think we've all been there!

Post by **millerman** » Mon Aug 10, 2009 9:52 pm

Try swapping the petrol pump from your other Minor, if it still doesn't perform then you've eliminated the pump causing the problem

Post by **Mick_Anik** » Mon Aug 10, 2009 11:29 pm

Good idea! I suppose you could swap everything, one thing at a time. Might be the quickest route to a solution.

Post by **Peetee** » Tue Aug 11, 2009 12:48 am

I'm tempted to think this is a fuel pump issue. A weak pump would cope with short high demand but begin to struggle with sustained load. If it is anything like the one I just removed from Albert (which looked fine - even the points) some trips would pass without incident and others would be a disaster. When it was replaced I was amazed how the car had been held back. He had so much more go.

Post by **MarkyB** » Tue Aug 11, 2009 9:02 am

There is a flow test for the pump.
I think it is 1 pint in 1 minute (it's in the book) anything less would show up as power loss at higher engine speeds.